The present application relates to a processing apparatus for forming a microscopic pattern on a surface of a work to be processed.
A technique of forming a microscopic pattern on a surface of a work is a backbone of an information industry in recent years owing to a functional surface that can be newly created thereby. For example, a Fresnel lens, a micro prism, and a micro lens array exhibit an optical function and are thus widely used in the information industry. For example, by forming a three-dimensional microscopic pattern on a surface of a work and distributing the three-dimensional microscopic pattern on a constituent of a display portion of an FPD (Flat Panel Display), it becomes possible to provide a display with a light source intensity distribution correction function, an antireflection function, a rainbow/moire prevention function, and the like. The three-dimensional microscopic pattern is also formed for increasing power generation of a solar cell expected as a clean energy.
In recent years, various FPDs are available, such as small or medium-sized FPDs to large-area FPDs, and the same holds true for solar cells. The three-dimensional microscopic pattern formed for the purpose of providing the optical function or increasing the power generation varies depending on a device size and purpose. Thus, there is needed a technique of forming microscopic patterns for various target specs.
In addition, the technique can also find application in suppressing a frictional force by forming a microscopic pattern on an engine piston sliding portion and reducing an area in contact, for improving a tribological function. It is also possible to, for improving an interfacial function, form a self-clean surface having water repellency improved by the microscopic pattern, or improve characteristics such as heat conductivity, boundary layer flow, bearing, antirust, and adhesion. Furthermore, the technique is now widely applied to implant, biosensor, and the like in a field of biotechnology.
As the technique of forming a microscopic pattern, a processing method by which a highly precise surface pattern can be formed across a large area in real time is desirable. As an electrical, optical technique of forming a three-dimensional microscopic pattern, there are known various methods such as an electron beam depiction method, a laser depiction method, and a holographic method. Those methods are effective in producing a structure having an extremely short spatial wavelength of a micrometer to submicrometer order, such as a non-reflective surface, a diffraction grating, and a micro lens array, but are unsuited for producing complicated three-dimensional patterns.
Meanwhile, owing to advancements of precise motion control and measurement/high-precision processing tools, current ultra-precise cutting/grinding processing techniques have enabled processing to be easily carried out with precision of a submicrometer order or less. A typical example of such processing is a single-point diamond cutting processing method that involves processing a soft metal or the like by use of a high-precision processing machine while using a single-crystal diamond tool having a single extremely-sharp cutting edge. In the method above, it is possible to three-dimensionally control a movement of the tool with respect to a workpiece with high precision and at high speed by using an FTS (Fast Tool Servo) technique or an FTC (Fast Tool Control) technique. Compared to the electrical, optical processing method, the diamond cutting processing method is suited for forming a three-dimensional microscopic pattern having a spatial wavelength ranging from several ten micrometers to several hundred micrometers.
In the normal cutting processing, three axes including two orthogonal axes and a rotation axis are controlled by a lathe to thus form a target pattern on the work. The FTC on the other hand is a technique of controlling one of the two orthogonal axes by a mechanism that has high resolution, rigidity, and responsiveness, such as a piezoelectric device. Unlike normal mechanical processing, the FTC technique having a characteristic of controlling a tool at high speed has an important object of accurately measuring a force that acts on the tool during processing, for producing a microscopic pattern with high precision.
In this regard, Japanese Patent Application Laid-open No. 2006-159299, for example, has proposed a processing apparatus having a structure in which an actuator, a tool holder, a displacement sensor, and a force sensor are formed integrally. The actuator is constituted of a piezoelectric device (PZT) for driving a tool. The tool holder is coupled to the actuator and holds the tool. The displacement sensor is disposed coaxially with the actuator and measures a displacement of the tool. The force sensor measures a force applied to the tool. The actuator causes the tool to vibrate microscopically so that a surface of a work is processed. A cutting force is detected as a value obtained by subtracting an output of the force sensor detected when no processing is carried out from an output of the force sensor detected during processing. The output of the force sensor detected when no processing is carried out refers to an output of the force sensor detected when the tool is caused to vibrate microscopically without being brought into contact with the work. Accordingly, in-process monitoring of the cutting force of the tool becomes possible.